Cooling apparatus and cooling method for heating elements

ABSTRACT

A cooling liquid  28  with a boiling temperature lower than the maximum allowed temperature for the operating atmosphere of switching elements  42  and which is highly insulative is used to liquid seal the switching elements  42.  This cooling liquid  28  is cooled by a liquid cooler  50.  The cooling liquid  28  vaporizes and removes the heat generated by the switching elements  42  to cool the switching elements  42.  Vaporized cooling liquid  28  is cooled by the liquid cooler  50  and is liquefied. The switching elements  42  can be efficiently cooled and the size of the apparatus can be reduced.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a cooling apparatus and acooling method for heating elements.

[0003] 2. Description of the Related Art

[0004] A type of cooling apparatus for heating elements has beenproposed in which IGBT elements (switching elements) used as heatingelements are cooled by an inverter constituted from the IGBT elementsmounted on an opening of a liquid cooling heat sink. This is describedin, for example, Japanese Patent Laid-Open Publication No. Hei 9-121557.In this apparatus, the heat generated by the IGBT elements istransferred to the liquid cooling heat sink by heat conduction andremoved by a cooling medium, such as water, flowing through a pathformed at the opening of the liquid cooling heat sink. Thereby, the IGBTelements are cooled.

[0005] Another cooling apparatus for heating elements is proposed inwhich semiconductor elements are liquid sealed by Freon and partitionsare provided between the semiconductor elements (for example, JapanesePatent Laid-Open Publication No. Sho 57-141945). In this apparatus, thesemiconductor elements are cooled by removing the heat of vaporizationof Freon from the semiconductor elements. In this apparatus, decrease incooling effect due to generation of film of bubbles between thesemiconductors is prevented by providing partitions.

[0006] However, in this type of apparatus for cooling IGBT elementsusing a liquid cooling heat sink, there is a problem that the IGBTelements cannot be effectively or sufficiently cooled. Especially inrecent years, there is a strong demand for reducing the size of alldevices including the inverter etc., and to fulfill this demand, theswitching elements of the inverter are closely packed. Therefore,although sufficient cooling of these switching elements remains arequirement, the amount of heat which can be removed by cooling usingheat conduction is not sufficient.

[0007] In the apparatus in which the semiconductor elements are liquidsealed by Freon, some of the semiconductor elements are released fromthe liquid sealing when the apparatus is tilted, thereby causing aproblem where the semiconductor elements are not sufficiently cooled.Moreover, when the semiconductor elements are used for long period oftime, the temperature of Freon reaches its boiling temperature causingintense vaporization, generating a vaporization film around thesemiconductor elements, and again causing a problem that thesemiconductor elements are not sufficiently cooled.

SUMMARY OF THE INVENTION

[0008] One object of a cooling apparatus of heating elements accordingto the present invention is to efficiently and sufficiently cool theheating elements. Another object of the cooling apparatus of heatingelements of the present invention is to sufficiently cool the heatingelements, even when the apparatus is tilted. A further object of thecooling apparatus of the heating elements of the present invention is areduction in size of the apparatus. One object of a cooling method ofheating elements according to the present invention is to provide amethod for efficiently and sufficiently cooling the heating elements.

[0009] In order to solve the objects mentioned above, the coolingapparatus and cooling method of the heating elements according to thepresent invention are configured as described below.

[0010] The heating element cooling apparatus according to the presentinvention is a cooling apparatus for cooling heating elements comprisinga liquid sealing container for liquid sealing said heating elementsusing a cooling liquid having a boiling temperature lower than theallowed temperature of operating atmosphere of said heating elements,and a cooling mechanism for cooling said cooling liquid.

[0011] With the heating element cooling apparatus of the presentinvention, the heating elements are cooled by removing the heat ofvaporization of the cooling liquid having a boiling temperature lowerthan the allowed temperature of operating atmosphere of the heatingelements directly or indirectly from the heating elements, therebyincreasing the cooling efficiency. Furthermore, the vaporized gas of thecooling liquid can be liquefied by cooling the gas with the coolingmechanism. The reliquefied gas can be re-used for cooling the heatingelements, placing the temperature of the operating atmosphere of theheating elements within the allowed temperature range.

[0012] In accordance with one aspect of the heating element coolingapparatus of the present invention, said liquid sealing container can bemeans for removing fluids other than said cooling liquid and for liquidsealing said heating elements using said cooling liquid. With thisconfiguration, the heating elements do not expose themselves out of thecooling liquid even when the apparatus is tilted, and the heatingelements can be cooled even in such a case.

[0013] In accordance with another aspect of the heating element coolingapparatus of the present invention, said liquid sealing container can bemeans having a flow path for the cooling medium used by said coolingmechanism. In this manner, the cooling liquid used for liquid sealingcan be cooled using the cooling medium.

[0014] In accordance with further aspect of the heating element coolingapparatus of the present invention, said heating elements can beswitching elements and said cooling liquid can be an insulator. Withthis configuration, electric short-circuiting by liquid sealing can beprevented. In the cooling apparatus of the heating elements of thisaspect of the present invention, said cooling liquid can be perfluorocarbon.

[0015] A heating element cooling method according to the presentinvention is a cooling method for cooling heating elements, comprisingthe steps of cooling said heating elements using the heat ofvaporization of a cooling liquid having a boiling temperature lower thanthe allowed temperature of the operating atmosphere of said heatingelements and contacting with at least some of said heating elements, andcooling said cooling liquid using a cooling medium different from saidcooling liquid.

[0016] With the heating element cooling method of the present invention,cooling can be efficiently performed because the heating elements arecooled by directly or indirectly removing the heat of vaporization ofthe cooling liquid having a boiling temperature lower than the allowedtemperature of the operating atmosphere of the heating elements from theheating elements. Moreover, by cooling the cooling liquid using acooling medium other than the cooling liquid, vaporized gas of thecooling liquid can be liquefied and the liquefied gas can be re-used forcooling the heating elements, thereby maintaining the temperature of theoperating atmosphere of the heating elements within the allowedtemperature range.

[0017] In accordance with one aspect of the cooling method of theheating elements of the present invention, said heating elements can beswitching elements and said cooling liquid can be an insulator. In thismanner, electric short-circuiting by the liquid sealing can beprevented. In the cooling method of heating elements of this aspect ofthe present invention, said cooling liquid can be perfluoro carbon.

BRIEF DESCRIPTION OF THE DRAWING

[0018]FIG. 1 is a structural diagram schematically showing an examplestructure of a cooling apparatus according to the preferred embodimentof the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT

[0019] The preferred embodiment of the present invention is describednext. FIG. 1 is a structural diagram schematically showing the structureof a cooling apparatus 20 for cooling switching elements 42 which areheating elements according to one embodiment of the present invention.As shown in the figure, the cooling apparatus 20 of this embodimentcomprises a box-shaped case 22 for storing a plurality of switchingelements 42 in a storage section 23, cooling liquid 28 filled into thestorage section 23 of the case 22, and a liquid cooler 50 for coolingthe cooling liquid 28.

[0020] The case 22 is provided with a flow path 26 in the outer wall fora cooling medium such as water. A flow-in end 24 and a flow-out end 25of the cooling medium are connected to a circulation tube 52 of theliquid cooler 50. The storage section 23 inside the case 22 is sealedand switching elements 42 are placed on a plate 40 by wire bonding 44 atthe bottom of the storage section 23. In this example, IGBT (InsulatedGate Bipolar Transistor) elements are used as the heating elements.Because the mounting substrate and electric wiring of the switchingelements 42 do not constitute the main section of the present invention,they are neither shown nor explained.

[0021] The cooling liquid 28 to be filled in the storage section 23 ofthe case 22 has a boiling temperature within the range of operatingatmosphere temperatures in which the switching elements can comfortablyoperate. This cooling liquid 28 also is highly insulative. In thepresent embodiment, perfluoro carbon (such as Frorinate manufactured bySumitomo 3M, Co.) which is highly insulative and the boiling temperatureof which is lower than the allowed temperature of the operatingatmosphere of IGBT. The cooling liquid 28 cools the switching elements42 by removing the heat generated by the switching elements 42 throughvaporization.

[0022] The liquid cooler 50 comprises a circulation tube 52 which isconnected to the flow-in end 24 and the flow-out end 25 of the case 22and which forms a circulation path with the flow path 26 of the case 22,a circulation pump 54 mounted on this circulation tube 52 forcirculating the cooling medium through the circulation tube 52, and aradiator 56 also mounted on the circulation tube 52 for cooling thecooling medium using the outside air. The liquid cooler 50 cools thecooling liquid 28 filling the storage section 23 of the case 22 bycirculating the liquid medium cooled by the outside air through thecirculation tube 52 using the circulation pump 54. Thus, the coolingliquid 28 which is vaporized by the heat of the switching elements 42 iscooled and liquefied by the liquid cooler 50.

[0023] With the heating element cooling apparatus 20 as described above,the switching elements 42 can be cooled by directly or indirectlyremoving the heat of vaporization of the cooling liquid 28 having aboiling temperature lower than the allowed temperature of the operatingatmosphere from the switching elements 42. Moreover, because the coolingliquid 28 is cooled by the liquid cooler 50, vaporized cooling liquid 28can be liquefied and re-used for cooling the switching elements 42. As aresult, the cooling efficiency can be improved and, at the same time,the size of the apparatus can be reduced. Furthermore, because thecooling liquid 28 is highly insulative, electric short circuiting doesnot occur. The temperature of the operating atmosphere of the switchingelements 42 can be placed within the allowed temperature range.

[0024] In the heating element cooling apparatus 20 as described, becausethe storage section 23 of the case 22 is formed to have a sealedstructure and is filled with the cooling liquid 28, the switchingelements 42 are not exposed out of the cooling liquid 28, even when thecooling apparatus 20 is tilted, enabling efficient cooling of theswitching elements 42 even under such conditions.

[0025] Even though the cooling apparatus 20 of heating elements of thepresent embodiment is constructed to cool the switching elements 42which are IGBT used as the heating elements, it can also be constructedto cool switching elements other than IGBT or to cool heating elementsother than switching elements.

[0026] In the heating element cooling apparatus 20 described above,perfluoro carbon is used as the cooling liquid 28 to fill the storagesection 23 of the case 22, but other liquid coolants can also be used aslong as they are sufficiently insulative and have a boiling temperaturewithin the allowed range of temperatures for the operating atmosphere ofthe switching elements 42. When it is not necessary to considerelectrical short-circuiting for the heating elements, the liquid neednot be highly insulative.

[0027] In the cooling apparatus 20 of heating elements of theembodiment, the flow path 26 for the cooling medium is provided on theouter wall of the case 22, but a tube can also be provided inside thestorage section 23 to form the flow path for the cooling medium.

[0028] The preferred embodiment of the present invention has beendescribed, but this description is not intended to limit the scope ofthe invention, and variations and modifications can be realized withinthe spirit and scope of the invention.

What is claimed is:
 1. A cooling apparatus for cooling heating elements, comprising, a liquid sealing container for liquid sealing heating elements using a cooling liquid having a boiling temperature within the allowed temperature range for the operating atmosphere of said heating elements, and a cooling mechanism for cooling said cooling liquid.
 2. A cooling apparatus of claim 1, wherein, said heating elements are switching elements and said cooling liquid is an insulator.
 3. A cooling apparatus of claim 2, wherein, said cooling liquid is perfluoro carbon.
 4. A cooling apparatus of claim 1, wherein, said liquid sealing container removes fluids other than said cooling liquid and liquid seals said heating elements using said cooling liquid.
 5. A cooling apparatus of claim 4, wherein, said heating elements are switching elements and said cooling liquid is an insulator.
 6. A cooling apparatus of claim 5, wherein, said cooling liquid is perfluoro carbon.
 7. A cooling apparatus of claim 1, wherein, said liquid sealing container has a flow path for a cooling medium used by said cooling mechanism.
 8. A cooling apparatus of claim 7, wherein, said heating elements are switching elements and said cooling liquid is an insulator.
 9. A cooling apparatus of claim 8, wherein, said cooling liquid is perfluoro carbon.
 10. A cooling method for cooling heating elements, comprising the steps of, cooling heating elements using the heat of vaporization of a cooling liquid having a boiling temperature within the allowed temperature range for the operating atmosphere of said heating elements and contacting with one or more of said heating elements, and cooling said cooling liquid using a cooling medium other than said cooling liquid.
 11. A cooling method of claim 10, wherein, said heating elements are switching elements and said cooling liquid is an insulator.
 12. A cooling method of claim 11, wherein, said cooling liquid is perfluoro carbon. 